Introduction Joints are the meeting points of two or more bones. Joints allow different parts of the body to move and they allow various planes of movement. Joints may allow extension, flexion, abduction, adduction, rotation or circumduction depending on the structure and shape of the bones involved. Joints are classified in three major ways. 1. The easiest way to classify joints is by the number of bones involved in a particular joint. A joint only involves two bones, while a joint involves three or more bones. 2. Another way to classify joints is to describe the function of a particular joint. A is an immobile joint, an is a slightly moveable joint and a is a freely moveable joint. 3. The final way to classify joints is by the structures involved in the joint. joint occurs where two or more bones are connected through fibrous connective tissue. Typically, these joints offer little range of motion and usually ossify with age. A joint occurs where two or more bones are united by fibrocartilage or hyaline cartilage plates. These joints generally offer a small range of motion. A joint occurs where two or more bones meet inside a joint capsule that is filled with synovial fluid. The articulating ends of the bones are covered in hyaline cartilage and the joint is typically supported by ligaments. Synovial joints generally offer a wide range of motion and are the type of joint responsible for most of the motility of the body. Synovial joints tend to be more prone to joint disease as this type of joint has a greater degree of motion and therefore a greater amount of stress. The typical structures found in a synovial joint are the: articular cartilage & subchondral bone joint cavity joint capsule fibrous layer synovial membrane synovial fluid which may be located inside the joint capsule or outside of the joint capsule. Some synovial joints involve fibrocartilage plates called which help increase the congruity of the articulating surfaces. Muscles and tendons span across synovial joints and contract or relax to move bones closer or farther from one another. During movement the joint acts as the pivot point for the bones. Most synovial joints are also supported by
137
Made with FlippingBook Publishing Software